Sound head for magnetic recording machine



. l V Jan 21 1941- H. s. HELLER 2,229,326

SOUND HEAD FOR MAGNETIC RECORDING MACHINE Original Filed 001'.. 25, 1937 2 Sheets-Sheet' l ,67H orney.

Jan. 21,

H. S. HELLER SOUND HEAD FOR MAGNETIC RECORDING MACHINE Patented Jan. 21, 1941 A UNITED STATES PATENT OFFICE Herman S. Heller, West Los Angeles, Calif.

Application October 25, 1937, Serial No. 170,985 Renewed July 10, 1940 6 Claims.

This invention relates generally to tone heads for magnetic sound recording machines.

In magnetic sound recording machines, a magnetic element, either a wire or a fiat tape, is driven at constant speed through a tone head between erasing and recording pole pieces surrounded and magnetized by coils mounted in the tone head, these coils carrying the erasing or recording currents. In certain forms of such machines, the pole pieces bear lightly on opposite sides of the recording element, and since the tips of the pole pieces which ride in engagement with the travelling recording elements are frequently of thickness dimensions as small as a few thousandths of an inch, it becomes desirable to inspect or replace the pole pieces from time to time. It also frequently becomes necessary to remove the magnetic tape from the machine and replace it by another, which necessitates either pulling the end of the used tape through the tone head, and inserting the end of a new tape therethrough, or else opening the tone head in such a manner that the tape can be moved transversely into and out of operative position between the coils.

It is accordingly one object of the present invention to provide a. tone head adapted to be opened up in an improved and highly convenient manner in order to expose thevpole tips for inspection or for pole piece replacement, or for convenient removal and replacement of the tape.

In accordance with the present invention, the coils and pole pieces on each side of the recording elements are mounted in an insulation block, and the two insulation blocks, on opposite sides of the recording element, are connected by pins tightly engaging one block and slidable in the other, these pins being provided with hinge joints. When it is desired to open the tone head, either for the purpose of replacement of the recording e1ement,'or for the purpose of inspecting or replacing the pole pieces, the two insulation blocks are rst pulled apart on these pins, and then swung apart in a jack-knife manner, thus opening up the tone head in such a 'manner that the pole pieces may be very conveniently observed or removed. If the purpose is simply to thread a different tape through the tone head, the two blocks may of course simply be pulled apart suiilciently for the purpose. without bending one of the blocks back on the hinge `ioints. In reclosing the tone head, the two coil-carrying blocks are rst swung into alinement, so that the pole tips are directly opposite one another, and then moved together on the mounting pins, this assuring that the pole tips move properly into engagement with the recording element, without binding or strain.

Various additional objects and corresponding features of the invention will appear and be more fully described in the course of the following detailed description of a present preferred embodiment thereof, reference for this purpose being had to the accompanying drawings, in which:

Fig. l is a front elevation of the tone head;

Fig. 2 is a longitudinal medial vertical section of the tone head, being taken as indicated by line 2 2 of Fig. 3;

Fig. 3 is a transverse section taken on line 3-3 of Fig. 2;

Fig. 4 is a. view taken as indicated by line 4 4 of Fig. 2;

Fig. 5 is a section taken 5 5 of Fig. 2;

Fig. 6 is a plan view of the tone head, with parts broken away, and showing the tone head in open position; f

Fig. 7 is a section taken on line 'l-l 6; and

Fig. 8 is a'perspective view of a typical pole piece.

The tone head here shown for illustrative purposes has a multiplicity of yerasing and recording coils, applicable for instance to a multiple lane as indicated by line of Fig.

recording system such as disclosed and claimed in a copending application led jointly by myself and Leo G. Butler, entitled Apparatus for Vmagnetic recordation and Areproduction of sound,

Serial No. 170,988, led Oct. 25, 1937. In such a system, the recording element is in the form of a flat tape, and a plurality of recordings are made on 'adjacent lanes of the tape, using for this purpose a plurality of sets of erasing and recording coils, Ithe central axes of which are latterly spaced from one another with reference to the magnetic tape, so as to act on adjacent recording lanes of the tape. While a tone head of the multiple lane recording -type is here shown for illustrative purposes, it will of course be evident that the provisions of the present invention are applicable as well to conventional magnetic recording systems in which a single line of recording is made on the recording element, which may be either a dat tape or a wire.

'I'he invention embodies two rectangular insulation blocks l0 and Il. A pair of headed pins I2, disposed at right angles to the meeting faces of blocks I0 and Il, pass with sliding fit through block Block l0 is thus movable towar'd and from block Il on pins i2, the opposing faces of the two blocks being in engagement with one another when the device is in operating position. Pins I2 have hinge joints I 3, permitting block I0 to be swung away from block Il after being outwardly on pins l2, in the manner illustrated in Fig. 6.

Block Il is mounted on the outer end of an electric plug member I6, which is adapted to be removably inserted in a socket member Il I ll and are tightly embedded in block II. r

mounted on a suitable support, as for instance a panel indicated in part at Ila. Leads from the erasing and recording coils are connected to pins I8 of plug members I5, which engage connector members I9 of socket member I1 when member I5 is inserted in I1. A suitable number of such pins and connectors are provided to take care of the leads from the erasing and recording coils. and also to take care of the ground lead coming from certain magnetic sheathing members, later to be mentioned. The opposed faces Illa and Ila of blocks III and II are formed with a longitudinally extending groove or way I5 adapted to receive and pass the recording element. For example. assuming use of a recording element in the form of a tape .002" in thickness and .125" in width, this way may be .003" in depth and .126" in width. The way should be only sufliciently larger than the crosssectional side ofthe tape to permit the tape to be drawn freely therethrough. The two blocks may be grooved in such a manner that the depth of this way I5 lies half withineach block when the two blocks are in face to face engagement.

Each end of block Il is formed, at opposite edges of way I5, with a pair of projections 20,'

and the projections 20 thus formed at each end of block II are received, when block I0 is moved into engagement with block I I, by a pair of complementary grooves or' recesses 2I. These projections 20 and grooves 2|, which slide together by a straight' line movement, necessitate that block I0 be moved on its hinge joints I3 into alinement with block II before being moved against block II. Block I0 thus comes into engagement with block II by movement straight toward said block II, this being desirable for reasons which will appear hereinafter.. Projections 20 are provided with a somewhat snugsliding fit within grooves 2|, and therefore serve to restrain the two. blocks against becoming slightly separated during operation.

Assuming that there are to be three recording lanes .on the lmagnetic tape, three sets'of recording and erasing coils are mounted in laterally offset positions in blocks I0 and II. The recording tape may be considered as divided laterally into two edge lanes anda middle lane, each of a width of one third the full width of the tape. Thus, a pair of erasing coils E1 and a pair of recording coils R1 are mounted in blocks I0 and II, with their axes in line with the center of one edge lane of the tape (see Figs. 3 and 4). A second pair of erasing coils E2 and a second pair of recording oo ils Rz are mounted in blocks I0 and II, with their axes in line with the center of the middle lane of the tape, and a third pair of erasing coils E: and a third pair of recording coils R3 are mounted in blocks III and I I, with their axes in line with the center of the other edge lane of the tape. Assuming, as typical, though not as essential, that the tape runs inan upward direction through the recording unit while a record is being made on the first edge lane of the tapeL travels downwardly through the recording unit while a record is being made on the second or middle lane, and again travels upwardly while a record is being made on the third edge lane, the relative disposition ofthe several coils -is typically as follows: Erasing coils E1 are located below recording coils Ri, erasing coils E: are located above recording coils R2, and erasing coils E: are located below recording coils Ra. Thus, when the tape travels upwardly for the purpose of recording on the first edge lane. it first passes erasing coils E1 and then recording coils R1; when the tape subsequently passes downwardly, for the purpose of recording on the middle lane, it first encounters erasing coils E: and then `recording coils Rz; and when the tape next travels upwardly for the purpose of recording on the opposite edge lanelit first encounters erasing coils Es and then recording coils Re.

Each of the recording and erasing coils comprises a wound magnetic bobbln 30 provided with a central aperture 3l of rectangular crosssection for the magnetic pole piece 32. Each bobbin 30 is received within a cylindrical magnetic sheath 33 mounted in insulation blocks III or II, as the case may be. sheaths 33 are interconnected by a grounded conductor 3l. Preferably, the inside flange 35 of each bobbin is provided with a pair of lips 36 adapted to be received within notches 31 formed in the insulation blocks III and Il in which the coils are mounted. These lips and notches are so related to the pole piece aperture 3| that when the bobbins are mounted in blocks I0 and II, apertures 3l are disposed exactly at right angles to the way I5 for the magnetic tape.

Pole pieces 32, of rectangular cross-section, are slidably mounted in apertures 3|, and their inner ends, which are preferably beveled and tapered to an edge preferably not over an approximate thickness of .003" and of a dimension at right angles to the tape approximately, or slightly less than, one-third ofthe-width of the tape (assuming three-lane recording). The pole piecesl may be formed initially with a comparatively sharp, chisel-like edge 32a, but by reason of wear on the tape are soon blunted somewhat and operate satisfactorily, with comparatively slow speed of tape, at a thickness dimension of approximately .003" as stated above.

"The outer ends of pole pieces 32 are engaged by plunger members 40 pressed lightly against the pole pieces by means of compression springs 4I mounted in housing l2 carried by plates 43 which are mounted on the insulation blocks, as in the manner clearlyillustrated in Fig. 2.

The tips of each pair of pole pieces are thus lightly pressed into contact with opposite sides of the recording tape, but are of such dimensions as to contact the tape only within the lane area within which said pole pieces are to act.

In the ,embodiment of the invention here shown, the pole pieces of each pair of erasing coils are somewhat offset from one another in a direction longitudinally of the tape, while each pair of recording coil pole pieces are directly opposite one another, as clearly indicated in Figs.

2 and 3. v

Preferably, rectangular, electrically grounded magnetic sheaths 45 and 46 are lplaced over blocks I0and Il, respectively, entirely enclosing said blocks except for their meeting faces. These sheaths serve to screen out extraneous magnetic fields which might otherwise cut the recording Acoils and produce noise. i

Electrical connections are made to each coil through suitable apertures in the outside flanges 35a of the coil bobbin, as indicated in Fig. 5. The outer face of each of blocks I0 and II is recessed, as indicated, to provide a 'surface 53 in the plane of outer bobbin flanges 35a, leaving a marginal portion 54 for support of plate-143. Leads 55 connected to the coils through suitable apertures in bobbin flanges 35a are receivedin grooves 56 formed in surfaces 53, said grooves leading to a longitudinally extending hollow 58 of sulcient cross-sectional area to carry the leads from all of the coils. The leads 55 running through hollow 58 in block I0 are gathered into a cable 6I extending through an aperture 62 in the rearward side of block I0 and entering a similar aperture 63 in the rearward side of block il. The entire set of leads 55 finally extend through the rearward side of block ii to connect to the various connector pins I8 of connector plug I6.

A feature of especial advantage in thetone head as now described is the novel means for moving the two members of the tone head apart when the magnetic tape is to be removed or replaced, or for the purpose of inspecting or replacing the pole pieces. If the tape is simply to be removed or replaced, block I0 may simply be pulled rearwardly on pins I2 until the tape clears projections 20. If the pole pieces are to be inspected or removed, block 20 is pulled outwardly until it engages pin heads I2, and is then swung rearwardly on hinges I3, thus exposing the pole piece tips so that they may be readily inspected or removed. It is a feature of the invention that block I0 must irst be swung into alinement with block II before it can be moved inwardly on pins I2 to its closed or operative position. This insures that the pole piece tips will always move straight toward the magnetic tape as the device is closed, thus avoiding binding or scraping of the pole piece tips on the tape as block` I0 comes against block II.

It will be understood that various changes in design, structure and arrangement may be made in the device without departing from the spirit and scope of the invention or of the appended claims, the device as here shown being simply illustrative and typical of the invention rather than. restrictive thereon.

I claim: v

1. A sound head comprising a pair of insula tion blocks normally occupying a position with opposing faces adjacent one another and adapted to have a recording element moved therebetween along a predetermined path, coils mounted in said blocks on opposite sides of said predetermined path, pole pieces in said coils adapted to contact opposite sides of the recording element, and means mountingone of said blocks on the other for movement rst straight away from said other block and then on an axis between said blocks.

2. A sound head comprising a pair of insulation blocks normally occupying a position with opposing faces adjacent one another and adapted to have a recording element moved therebetween along a predetermined path. coils mounted in said blocks on opposite sides of said predetermined path. pole pieces in said coils adapted to contact opposite sides of the recording element. and means mounting one of said blocks on the other for movement toward and from said other block, said means comprising a plurality of pins rigidly mounted in one of the blocks and extending substantially at right angles to the meeting faces of said blocks, with sliding ilt in the other block.-

3. A sound head comprising a pair of insulation blocks normally occupying a position with 'opposing faces adjacent one another and adapted to have a recording element moved therebetween along a predetermined path, coils mounted in said blocks on opposite sides of said predetermined path, pole pieces in said coils adapted to contact opposite sides of the recording element, and means mounting one of said blocks'on the other for movement toward and from said other block, said means comprising a plurality 'oi' pins rigidly mounted in one of the blocks and extending substantially at right angles to the meeting faces of said blocks, with sliding llt in the other block, and hinge' joints in said pins permitting said blocks to be swung apart.

4. A sound headcomprising a pair of insula-l tion blocks normally occupying a position with opposing faces adjacent one another and adapted to have a recording element moved therebetween along a predetermined path, coils mounted in said blocks onV opposite sides of said predetermined path, pole pieces vin said coils adapted to contact opposite sides of the recording element, and means mounting one of said blocks on the other for movement toward and from said other block, said means comprising a plurality of pins rigidly mounted in one of the blocks and extending substantially at right angles to the meeting `faces of said blocks, wth sliding fit in the other block, and hinge joints in said pins at points normally located within said last mentioned block but cleared by said block after a predetermined separation of the blocks to permit said last mentioned block to be swung away from said other block.

5. A sound head comprising a pair of insulation blocks, adapted to be positioned with their opposing faces adjacent one another, there being a way between said opposing faces for a travelling recording tape, coils mounted in said blocks on opposite sides of said way, said coils comprising magnetic bobbins having flanges itted in said blocks, and windings surrounding said bobbins, a formation on at least one ange of each bobbin and a complementary formation on the corresponding block, whereby said bobbins flt in predetermined positions in said blocks, a pole piece aperture extending axially through each. of said bobbins, said apertures being substantially rectangular in cross-section, and being so placed in the bobbins that their direction of elongation is dispod substantially at right angles to said way? when the bobbins are mounted in the blocks, and pole pieces substantially rectangular in crosssection slidably mounted in said apertures and adapted to bear on opposite sides of a tape travelling through said way.

6. 'A sound head comprising a pair of mountings. coils supported on said mountings in end to end opposition. pole pieces coaxially arranged in said coils adapted to contact opposite sides of a magnetic record element running therebetween. said mountinss being adapted to occupy a normal operating position with the ends of said coils closely spaced from one another andV with said pole pieces in engagement with opposite .Y

sides ot saidi record element, and means mounting one of said mountings ior opening movement tawaytromsaidothermountingonA adirectionlinsparalleltotheaxesotsaidcoils and then on a pivot axisnormal to said direction line.

HERMAN 8. HEUER. 

